Imaging apparatus and focus control method

ABSTRACT

There is provided an imaging apparatus including a first focus detection unit that has a plurality of first focus detection areas in a photographed screen, and detects a first defocusing amount in the first focus detection areas, a second focus detection unit that has a plurality of second focus detection areas in a photographed screen, and detects a second defocusing amount in the second focus detection areas, a defocusing amount selection unit that selects which of the first defocusing amount detected by the first focus detection unit and the second defocusing amount detected by the second focus detection unit is used, and a focus control unit that performs focus control by moving a focus lens on the basis of the defocusing amount selected by the defocusing amount selection unit.

TECHNICAL FIELD

The present technology relates to an imaging apparatus and a focuscontrol method.

BACKGROUND ART

In single lens reflex cameras of the related art, a so-called dedicatedphase difference sensor is mounted to realize fast autofocus. On theother hand, compact cameras, mirrorless cameras, and the like generallyemploy a contrast detection autofocus (hereinafter referred to as AF)system. In addition, in order to realize fast AF in such cameras, amethod of embedding an image sensor for phase difference detection inanother image sensor has been proposed (Patent Literature 1).

Furthermore, a method of mounting both a dedicated phase differencedetecting module and a phase difference detecting image sensor has alsobeen proposed in order to obtain advantages of both sensors using theabove-described technique (Patent Literature 2).

CITATION LIST Patent Literature

Patent Literature 1: JP 2000-156823A

SUMMARY OF INVENTION Technical Problem

AF areas that support as wide regions as possible are desired for suchcameras to allow for AF tracing of subjects moving up and down, andsideways. Accordingly, if both of a dedicated phase difference detectingmodule and a phase difference detecting image sensor are mounted tosupport a wide range of areas, the difficulty is expected in focusing ontargeted subjects through wide detection. It is also conceivable thatthe entrance of an unintended subject into the frame easily shifts thefocus to the subject.

In view of these problems, the present technology has been devised. Thepurpose of the present technology is to provide an imaging apparatus anda focus control method that can keep tracing a target subject.

Solution to Problem

To solve the above-described problems, the first technology provides animaging apparatus including a first focus detection unit that has aplurality of first focus detection areas in a photographed screen, anddetects a first defocusing amount in the first focus detection areas, asecond focus detection unit that has a plurality of second focusdetection areas in a photographed screen, and detects a seconddefocusing amount in the second focus detection areas, a defocusingamount selection unit that selects which of the first defocusing amountdetected by the first focus detection unit and the second defocusingamount detected by the second focus detection unit is used, and a focuscontrol unit that performs focus control by moving a focus lens on thebasis of the defocusing amount selected by the defocusing amountselection unit.

Furthermore, the second technology provides a focus control methodincluding selecting which of a first defocusing amount and a seconddefocusing amount is used, the first defocusing amount being detected bya first focus detection unit that has a plurality of first focusdetection areas in a photographed screen, the second defocusing amountbeing detected by a second focus detection unit that has a plurality ofsecond focus detection areas in a photographed screen, and performingfocus control by moving a focus lens on the basis of the selecteddefocusing amount.

Advantageous Effects of Invention

According to the present technology, it is possible to keep tracing atarget subject when an imaging apparatus images an image.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of an imagingapparatus according to a first embodiment of the present technology.

FIG. 2 is a schematic cross-sectional diagram illustrating a schematicconfiguration of an imaging apparatus.

FIG. 3 is a diagram illustrating a configuration of an image sensor.

FIG. 4 is a diagram illustrating a disposition of image-plane AF areasand dedicated AF areas on a photographed screen.

FIG. 5 is a diagram for describing a configuration of image-plane AFareas.

FIG. 6 is a diagram for describing another configuration of image-planeAF areas.

FIGS. 7A, 7B, 7C, and 7D are diagrams for describing an overview of aprocess in the first embodiment.

FIGS. 8A, 8B, 8C, and 8D are diagrams for describing an overview ofanother process in the first embodiment.

FIG. 9 is a diagram for describing an overview of still another processin the first embodiment.

FIG. 10 is an overall flowchart for describing the processes in thefirst embodiment.

FIG. 11 is a flowchart for describing a defocusing amount selectionprocess in the first embodiment.

FIG. 12 is a flowchart for describing a stabilization process.

FIG. 13 is a flowchart for describing an image-plane defocusing amountdecision process in the first embodiment.

FIG. 14 is a flowchart for describing a previously decided image-planedefocusing amount determination process.

FIG. 15 is a flowchart for describing an image-plane defocusing amountcorrection process.

FIG. 16 is a flowchart for describing the image-plane defocusing amountcorrection process.

FIG. 17 is a block diagram illustrating a configuration of an imagingapparatus according to a second embodiment of the present technology.

FIGS. 18A, 18B, 18C, and 18D are diagrams for describing a first exampleof an overview of a process in the second embodiment.

FIGS. 19A, 19B, 19C, and 19D are diagrams for describing a secondexample of the overview of the process in the second embodiment.

FIG. 20 is a flowchart for describing another defocusing amountselection process in the first embodiment.

FIG. 21 is a flowchart for describing the defocusing amount selectionprocess in the first embodiment.

FIG. 22 is a flowchart for describing an image-plane defocusing amountdecision process in the second embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present technology will be describedwith reference to the appended drawings. Note that the description willbe provided in the following order.

-   <1. First Embodiment>-   [1-1. Configuration of Imaging Apparatus]-   [1-2. Overview of Process]-   [1-3. Defocusing Amount Selection Process]-   [1-4. Image-plane Defocusing Amount Decision Process]-   [1-5. Image-plane Defocusing Amount Correction Process]-   <2. Second Embodiment>-   [2-1. Configuration of Imaging Apparatus]-   [2-2. Overview of Process]-   [2-3. Defocusing Amount Selection Process]-   <3. Modified example>    <1. First Embodiment>    [1-1. Configuration of Imaging Apparatus]

The configuration of an imaging apparatus 1000 according to the presentembodiment will be described. FIG. 1 is a diagram illustrating a blockconfiguration of the imaging apparatus 1000. FIG. 2 is a schematiccross-sectional diagram illustrating a schematic configuration of theimaging apparatus 1000.

The imaging apparatus 1000 of FIG. 6 is configured to include theoptical imaging system 1011, the dedicated AF sensor 1020, the imagesensor 1030, the image-plane AF sensor 1031, a pre-processing circuit1040, a camera processing circuit 1050, an image memory 1060, a controlunit 1070, a graphic I/F (Interface) 1080, a display unit 1090, an inputunit 1100, an R/W (reader and writer) 1110, and a storage medium 1120.The control unit functions as a defocusing amount computation unit 1071,a defocusing amount selection unit 1072, a defocusing amount decisionunit 1073, a defocusing amount correction unit 1074, and a focus controlunit 1075.

The optical imaging system 1011 is configured to include thephotographing lens 1011 for collecting light from a subject on the imagesensor 1030 (including a focus lens, a zoom lens, and the like), a lensdrive mechanism 1012 that adjusts focus by moving the focus lens, ashutter mechanism, an iris mechanism, and the like. The system is drivenbased on a control signal from the control unit 1070 and the focuscontrol unit 1075. The lens drive mechanism 1012 realizes an AFoperation by moving the photographing lens 1011 in an optical axisdirection by an amount corresponding to a defocusing amount suppliedfrom the focus control unit 1075. A light image of a subject obtainedthrough the optical imaging system 1011 is formed on the image sensor1030 serving as an imaging device.

The dedicated AF sensor 1020 is a dedicated autofocus sensor of, forexample, the phase difference detection AF system, the contrastdetection AF system, or the like. Subject light collected by thephotographing lens 1011 is reflected on the semi-transmissible mirrorand incident on the dedicated AF sensor 1020. A focus detection signaldetected by the dedicated AF sensor 1020 is supplied to the defocusingamount computation unit 1071. The dedicated AF sensor 1020 correspondsto a first focus detection unit according to the claims. Thus, adefocusing amount obtained from detection of focus by the dedicated AFsensor 1020 corresponds to a first defocusing amount according to theclaims.

The image sensor 1030 has R (Red) pixels, G (Green) pixels, and B (Blue)pixels, which are normal imaging pixels, and phase difference detectionpixels for detecting a phase difference focus. The pixels constitutingthe image sensor 1030 photoelectrically convert light incident from asubject into an amount of electric charge, and output a pixel signal. Inaddition, the image sensor 1030 finally outputs an imaging signal thatincludes the pixel signal to the pre-processing circuit 1040. As theimage sensor 1030, a CCD (Charge Coupled Device), a CMOS (ComplementaryMetal Oxide Semiconductor), or the like is used. It should be noted thata detailed configuration of the image sensor 1030 will be describedlater.

The image-plane AF sensor 1031 is a sensor for autofocus that includes aplurality of phase difference detection pixels. A focus detection signaldetected by the image-plane AF sensor 1031 is supplied to the defocusingamount computation unit 1071. A detailed configuration of theimage-plane AF sensor 1031 will be described later. The image-plane AFsensor 1031 corresponds to a second focus detection unit according to anembodiment of the present disclosure. Thus, a defocusing amount obtainedfrom detection of focus by the image-plane AF sensor 1031 corresponds toa second defocusing amount according to the claims.

The pre-processing circuit 1040 performs sample holding or the like onthe imaging signal output from the image sensor 1030 so that an S/N(Signal to Noise) ratio is satisfactorily held from a CDS (CorrelatedDouble Sampling) process. Furthermore, gain is controlled in an AGC(Auto Gain Control) process, A/D (Analog to Digital) conversion isperformed, and a digital image signal is thereby output.

The camera processing circuit 1050 performs signal processes such as awhite balance adjustment process, a color correction process, a gammacorrection process, a Y/C conversion process, an AE (Auto Exposure)process, and the like on the image signal output from the pre-processingcircuit 1040.

The image memory 1060 is a volatile memory, or a buffer memoryconfigured as, for example, a DRAM (Dynamic Random Access Memory), whichtemporarily stores image data that has undergone the predeterminedprocesses by the pre-processing circuit 1040 and the camera processingcircuit 1050.

The control unit 1070 is constituted by, for example, a CPU, a RAM, aROM, and the like. The ROM stores programs read and operated by the CPU,and the like. The RAM is used as a work memory of the CPU. The CPUcontrols the entire imaging apparatus 1000 by executing variousprocesses according to the programs stored in the ROM and issuingcommands.

In addition, the control unit 1070 functions as the defocusing amountcomputation unit 1071, the defocusing amount selection unit 1072, thedefocusing amount decision unit 1073, the defocusing amount correctionunit 1074, and the focus control unit 1075 by executing a predeterminedprogram. Each of the units may be realized by hardware with each of thefunctions as a dedicated device, not by a program. In this case, theimaging apparatus 1000 is configured to include the hardware.

The defocusing amount computation unit 1071 computes a defocusing amountthat indicates a deviation amount from focus based on a phase differencedetection signal acquired by the dedicated AF sensor 1020 or theimage-plane AF sensor 1031. The defocusing amount selection unit 1072performs a process of selecting which amount between a defocusing amountobtained from a detection result of the dedicated AF sensor 1020(hereinafter referred to as a dedicated defocusing amount) and adefocusing amount obtained from a focus detection result of theimage-plane AF sensor 1031 (hereinafter referred to as an image-planedefocusing amount) will be used in focus control and employing theresult. A detailed process performed by the defocusing amount selectionunit 1072 will be described later.

The defocusing amount decision unit 1073 performs a process of decidinga defocusing amount for each image-plane AF area based on theimage-plane defocusing amount computed based on the focus detectionresult of the image-plane AF sensor. A detailed process of thedefocusing amount decision unit 1073 will be described later. Thedefocusing amount correction unit 1074 performs a correction process ofan image-plane defocusing amount. A detailed process performed by thedefocusing amount correction unit 1074 will be described later. Thefocus control unit 1075 controls the lens drive mechanism 1012 of theoptical imaging system 1010 based on the employed defocusing amount toperform a focus adjustment process.

The graphic I/F 1080 causes an image to be displayed by generating animage signal for displaying the image on the display unit 1090 from theimage signal supplied from the control unit 1070 and supplying thesignal to the display unit 1090. The display unit 1090 is a display unitconfigured as, for example, an LCD (Liquid Crystal Display), a PDP(Plasma Display Panel), an organic EL (Electro-luminescence) panel, orthe like. The display unit 1090 displays a through image being captured,an image recorded in the storage medium 1120, and the like.

The input unit 1100 includes, for example, a power button for switchingbetween on and off of power, a release button for instructing start ofrecording a captured image, an operator for zoom adjustment, a touchscreen integrated with the display unit 1090, and the like. When aninput operation is performed on the input unit 1100, a control signalaccording to the input is generated and output to the control unit 1070.Then, the control unit 1070 performs an arithmetic operation process andcontrol according to the control signal.

The R/W 1110 is an interface connected to the recording medium 22 inwhich image data generated from imaging, and the like is recorded. TheR/W 1110 writes data supplied from the control unit 1070 on the storagemedium 1120, and outputs data read from the storage medium 1120 to thecontrol unit 1070. The storage medium 1120 is a large-capacity storagemedium 1120, for example, a hard disk, a Memory Stick (registeredtrademark of Sony Corporation), an SD memory card, or the like. Imagesare stored in a compressed state in the form of, for example, JPEG, orthe like. In addition, EXIF (Exchangeable Image File Format) dataincluding information of the stored images and additional informationsuch as imaged dates, and the like is also stored therein in associationwith the images.

Herein, a basic operation of the imaging apparatus 1000 described abovewill be described. Before an image is captured, signals obtained fromphotoelectric conversion of light sensed by the image sensor 1030 aresequentially supplied to the pre-processing circuit 1040. Thepre-processing circuit 1040 performs a CDS process, an AGC process, andthe like on the input signals, and further performs conversion of thesignals into image signals.

The camera processing circuit 1050 performs an image quality correctionprocess on the image signals supplied from the pre-processing circuit1040, and supplies the result to the graphic I/F 1080 via the controlunit 1070 as signals of a camera through image. Accordingly, the camerathrough image is displayed on the display unit 1090. A user can adjustan angle of view while viewing the through image displayed on thedisplay unit 1090.

In this state, when the shutter button of the input unit 1100 ispressed, the control unit 1070 outputs a control signal to the opticalimaging system 1011101 to cause a shutter included in the opticalimaging system 1011101 to operate. Accordingly, image signals for oneframe are output from the image sensor 1030.

The camera processing circuit 1050 performs an image quality correctionprocess on the image signals for one frame supplied from the imagesensor 1030 via the pre-processing circuit 1040, and supplies theprocessed image signals to the control unit 1070. The control unit 1070encodes and compresses the input image signals and supplies thegenerated encoded data to the R/W 1110. Accordingly, a data file of acaptured still image is stored in the storage medium 1120.

Meanwhile, when the image file stored in the storage medium 1120 isreproduced, the control unit 1070 reads the selected still image filefrom the storage medium 1120 through the R/W 1110 according to an inputoperation on the input unit 1100. The read image file is subjected to anextended decoding process. Then, decoded image signals thereof aresupplied to the graphic I/F 1080 via the control unit 1070. Accordingly,a still image stored in the storage medium 1120 is displayed on thedisplay unit 1090.

Next, the configurations of the image sensor 1030 and the image-plane AFsensor 1031 will be described. FIG. 3 is a diagram illustrating thearrangement of general pixels and phase difference detection pixels inthe image sensor 1030. R indicates R (Red) pixels, G indicates G (Green)pixels, and B indicates B (Blue) pixels, all of which are generalimaging pixels.

In addition, in FIG. 3, P1 indicates a first phase difference detectionpixel, and P2 indicates a second phase difference detection pixel. Thephase difference detection pixels are configured to form pairs of P1 andP2, and perform pupil-dividing of the photographing lens 1011. The phasedifference detection pixels P1 and P2 have an optical feature differentfrom general imaging pixels. It should be noted that, in FIG. 3, Gpixels are set as phase difference detection pixels. This is becausethere are twice as many G pixels as there are R pixels or B pixels.However, phase difference detection pixels are not limited to the Gpixels.

The image sensor 1030 has the phase difference detection pixels inaddition to the general pixels, and the imaging apparatus 1000 canperform so-called image-plane phase difference AF (Autofocus) using anoutput from the phase difference detection pixels.

FIG. 4 is a diagram illustrating AF areas of the dedicated AF sensor1020 on a photographed screen (hereinafter referred to as dedicated AFareas) and AF areas of the image-plane AF sensor 1031 on thephotographed screen (hereinafter referred to as image-plane AF areas).Additionally, the dedicated AF area corresponds to the first focusdetection area in the claims, and the image-plane AF area corresponds tothe second focus detection area in the claims.

In FIG. 4, the areas indicated by square frames are the dedicated AFareas. As understood from FIG. 4, the dedicated AF areas are disposed ina narrower range than the image-plane AF areas, and concentratedsubstantially in the vicinity of the center. The dedicated AF sensor1020 can detect a focus with higher accuracy than the image-plane AFsensor 1031.

The areas indicated by crosses in FIG. 4 are the image-plane AF areas.As understood from FIG. 4, the image-plane AF areas are spread in a widerange, and can complement a subject in a wide range.

There are cases in which it is difficult to uniformly dispose the AFareas at an equal interval in the dedicated AF sensor 1020 due todisposition of the areas in a dedicated optical system. For this reason,when detection results of the dedicated AF areas and the image-plane AFareas are compared as in the present technology, it is better to put thepositions of the two kinds of AF areas together. To this end, theimage-plane AF areas are unevenly disposed so that the positions of theimage-plane AF areas are associated with the positions of the dedicatedAF areas as shown in FIG. 4.

The phase difference detection pixels are embedded in image sensors 1030as shown in, for example, FIG. 5 so as not to affect a photographedimage. In the horizontal direction, a pair of elements (P and Q in thedrawing) that are partially opened and pupil-divided for detecting aphase difference are disposed in line. In addition, in the verticaldirection, lines of the phase difference pixels are embedded at aninterval of several lines.

In the phase difference detection pixels disposed as described above, aplurality of phase difference detection elements are set to be an AFarea as a group (for example, the rectangular frame indicated by a thickline in FIG. 5), and an arithmetic operation for focus detection isperformed for each area. Accordingly, by deviating setting of the AFareas as shown in FIG. 6, uneven disposition of the AF areas as shown inFIG. 4 is possible. It should be noted that the disposition of the AFareas can be unevenly made from a process of software, but by settingdisposition of the phase difference detection pixels in the image sensor1030 to be uneven, the AF areas can also be unevenly disposed.

[1-2. Overview of Process]

Next, a process executed by the imaging apparatus 1000 will bedescribed. First, an overview of a focusing process executed in thepresent embodiment will be described with reference to FIGS. 7 to 9.FIGS. 7 to 9 show dedicated AF areas within a photographed screen,image-plane AF areas within the photographed screen, and a subjecttraced using autofocus. In FIGS. 7 to 9, dashed-lined squares indicatethe dedicated AF areas of the dedicated AF sensor 1020, and dashed-linedcrosses indicate the image-plane AF areas of the image-plane AF sensor1031.

First, FIG. 7A shows a state in which a subject is not present andautofocus is not performed. When a subject appears as shown in FIG. 7B,and a user inputs an AF instruction (for example, half-presses ashutter), a defocusing amount is first computed based on a focusdetection result of the dedicated AF sensor 1020, and focus is set to beon a proximate subject (hereinafter referred to as a proximate subject)based on the defocusing amount. To be specific, focus is set to be onthe proximate subject by adjusting focus of the photographing lens 1011when the photographing lens 1011 is driven based on the defocusingamount. In FIG. 7, AF areas in which focus is on the proximate subjectare indicated by solid lines.

FIG. 7C shows a case in which the subject moves after focus is on theproximate subject. Also in this case, focus is adjusted so that thesubject proximate to a current focus position (subject with a minimumdefocusing amount) is kept to be focused using the defocusing amountcomputed based on respective focus detection results of the dedicated AFsensor 1020 and the image-plane AF sensor 1031. In FIG. 7C, a dedicatedAF area and image-plane AF areas in which the proximate subject isfocused are all indicated by solid lines.

FIG. 7D shows a case in which the subject moves and then leaves all AFareas of the dedicated AF sensor 1020. In this case, if the subject ispositioned within an image-plane AF area, focus is kept to be on thesubject with a minimum defocusing amount using the defocusing amount ofthe image-plane AF sensor 1031. Thus, focus is not lost from a subject.

In FIG. 7D, crosses of AF areas in which focus is on the subject areindicated by solid lines. It should be noted that, in the presenttechnology, when a subject leaves all dedicated AF areas and ispositioned only on image-plane AF areas, a process of increasingaccuracy of a defocusing amount is performed by the defocusing amountcorrection unit. Details of the process will be described.

FIG. 8A shows a case in which the subject further moves, and leaves allAF areas of the dedicated AF sensor 1020 and the image-plane AF sensor1031. In this case, the focus adjustment process is paused for apredetermined time at the final focus position until the subject isdetected again by the dedicated AF sensor 1020.

When the subject within a predetermined defocusing amount is notdetected by the dedicated AF sensor 1020 even after the predeterminedtime elapses from the pause of the focus adjustment, focus adjustment isperformed so as to focus on another subject with a minimum defocusingamount of the dedicated AF sensor 1020 as shown in FIG. 8B. Accordingly,a subject being traced is changed. In FIG. 8B, the cross of an AF areain which focus is on the subject is indicated by a solid line.

Even when the subject that was previously focused and traced enters AFareas of the dedicated AF sensor 1020 again as shown in FIG. 8C afterthe subject being traced is changed, focus adjustment is performed sothat focus is on the changed subject.

It should be noted that, when the subject being traced is not a subjectthat a user desires, the input of the AF instruction is first releasedby the user (for example, release of half-pressing of the shutter) topause the autofocus process. Then, there is no focus on any subject asshown in FIG. 8D.

In addition, when the user inputs an AF instruction again (for example,half-presses the shutter), focus adjustment is performed so that focusis on the proximate subject as shown in FIG. 9.

In the present technology as described above, a subject can be focusedand traced with high accuracy by using the dedicated AF sensor 1020 andthe image-plane AF sensor 1031 together.

FIG. 10 is an overall flowchart for describing the processes performedby the imaging apparatus 1000 as shown in FIGS. 7 to 9.

First, in Step S1, the defocusing amount computation unit 1071 computesdefocusing amounts. The computation of the defocusing amounts isperformed based on each of a focus detection result of the image-planeAF sensor 1031 and a focus detection result of the dedicated AF sensor1020. In other words, a defocusing amount is computed based on the focusdetection result of the image-plane AF sensor 1031 and a defocusingamount is computed based on the focus detection result of the dedicatedAF sensor 1020.

Next, in Step S2, the defocusing amount selection unit 1072 performs adefocusing amount selection process. The defocusing amount selectionprocess is a process of selecting which of the defocusing amounts of theimage-plane AF sensor 1031 and the dedicated AF sensor 1020 will be usedin focus control as a defocusing amount. Details of the defocusingamount selection process will be described later.

Next, in Step S3, the focus control unit 1075 controls driving of thefocus lens based on the defocusing amount selected from the defocusingselection process. Accordingly, focus control is performed. Furthermore,a focus determination process in Step S4 is a process of checkingwhether or not focus is on a subject that a user desires in a focusadjustment process. In the imaging apparatus 1000, the process isrepeated as long as the user inputs an AF instruction (for example,half-presses the shutter).

[1-3. Defocusing Amount Selection Process]

Next, the defocusing amount selection process included in the overallflowchart described above will be described with reference to theflowchart of FIG. 11. First, in Step S101, it is determined whether ornot a focus detection result of the image-plane AF sensor 1031 is valid.This determination is made based on, for example, a set state of theimaging apparatus 1000 by a user. The determination based on the setstate is made by confirming which mode the user has selected when theimaging apparatus 1000 is configured to select an AF mode in which theimage-plane AF sensor 1031 and the dedicated AF sensor 1020 are usedtogether or another AF mode in which only the dedicated AF sensor 1020is used. The detection result of the image-plane AF sensor 1031 isdetermined to be valid when a mode in which both sensors are used isselected, and the focus detection result of the image-plane AF sensor1031 is not valid when the AF mode in which only the dedicated AF sensor1020 is selected.

In addition, the determination of Step 101 may be made based on, forexample, whether or not the detection result of the image-plane AFsensor 1031 can be used at an exposure timing. The exposure timing ofthe image-plane AF sensor 1031 is not synchronized with the dedicated AFsensor 1020 since reading of imaging is restricted. Thus, when adetection timing (timing of exposure end) of the image-plane AF sensor1031 is acquired, and exposure timings are significantly deviated at atiming of exposure end of the dedicated AF sensor 1020, the focusdetection result of the image-plane AF sensor 1031 is not employed. Inthis manner, when the determination of Step S101 is performed, and thedetection result of the image-plane AF sensor 1031 is not valid, theprocess proceeds to Step S102 (No in Step S101).

Then, in Step S102, a proximate defocusing amount among a plurality ofdefocusing amounts computed based on detection results of a plurality ofdedicated AF areas is selected as a defocusing amount to be used infocus control (hereinafter the selected defocusing amount is referred toas a selected defocusing amount). When there are 11 AF areas of thededicated AF sensor 1020 as shown in FIG. 4, for example, the proximatedefocusing amount among the 11 defocusing amounts is set to be aselected defocusing amount.

Description will return to Step S101. In Step S101, when the detectionresult of the image-plane AF sensor 1031 is determined to be valid, theprocess proceeds to Step S103 (Yes in Step S101). Then, an image-planedefocusing amount decision process is performed in Step S103. Theimage-plane defocusing amount decision process is a process of computingdefocusing amounts for each of a plurality of image-plane AF areas(hereinafter referred to as image-plane defocusing amounts), anddeciding an image-plane defocusing amount. Details of the image-planedefocusing amount decision process will be described later.

When an image-plane defocusing amount is decided, it is checked whetheror not the imaging apparatus 1000 is in a proximity priority mode nextin Step S104. The proximity priority mode is a mode in which focus is ona most proximate subject within all focus areas. When the imagingapparatus 1000 is in the proximity priority mode (Yes in Step S104), thevalue of a proximate defocusing amount among defocusing amounts of thededicated AF areas (hereinafter referred to as dedicated defocusingamounts) is selected as a selected defocusing amount in Step S105. Thisis because a value of a proximate defocusing amount among the defocusingamounts is set to be selected according to the mode when the imagingapparatus 1000 is in the proximity priority mode. On the other hand,when the imaging apparatus 1000 is found not in the proximity prioritymode in Step S104, the process proceeds to Step S106 (No in Step S104).

Next, in Step S106, it is determined whether or not the dedicateddefocusing amounts obtained by the dedicated AF sensor 1020 are equal toor smaller than a first threshold value that is a predeterminedthreshold value. This determination is made on all of the dedicateddefocusing amounts. When the dedicated defocusing amounts are equal toor smaller than the first threshold value, the process proceeds to StepS107 (Yes in Step S106), and a minimum amount among the dedicateddefocusing amounts obtained for each of the plurality of dedicated AFareas is selected as a selected defocusing amount.

On the other hand, when the dedicated defocusing amounts obtained by thededicated AF sensor 1020 are equal to or greater than the firstthreshold value, the process proceeds to Step S108 (No in Step S106).Next, in Step S108, it is determined whether the defocusing amountsobtained by the image-plane AF sensor 1031 are equal to or smaller thana second threshold value that is a predetermined threshold value. Whenthe defocusing amounts are equal to or smaller than the second thresholdvalue, the process proceeds to Step S109 (Yes in Step S108), and aminimum amount among the image-plane defocusing amounts obtained foreach of the plurality of image-plane AF areas is selected as a selecteddefocusing amount.

On the other hand, when the defocusing amounts of the image-plane AFsensor 1031 are determined to be equal to or greater than the secondthreshold value in Step S108, the process proceeds to Step S110 (No inStep S108). Then, in Step S110, a minimum amount among the defocusingamounts obtained for each of the plurality of dedicated AF areas isselected as a selected defocusing amount. Next, a stabilization processis performed in Step S111.

Herein, the stabilization process will be described with reference tothe flowchart of FIG. 12. The stabilization process is a process ofemploying a selected defocusing amount as is only when the defocusingamount is not significantly changed. Accordingly, focus control can bestabilized without sharply changing a defocusing amount by a greatamount.

First, in Step S201, it is determined whether or not the selecteddefocusing amount is a value in a predetermined reference range. Whenthe defocusing amount is in the reference range, the process proceeds toStep S202, and a count value is set to be 0. This count value will bedescribed later. Then, next in Step S203, the selected defocusing amountis employed as a defocusing amount to be used in focus control. In StepS203, the defocusing amount to be used in focus control is decided. Theemployed defocusing value is supplied to the focus control unit 1075.

Description will return to Step S201. In Step S201, when the selecteddefocusing amount is determined not to be in the reference range, theprocess proceeds to Step S204 (No in Step S201). Next, in Step S204, itis checked whether or not a defocusing amount of an object (for example,the face of a person, or the like) is obtained. When a defocusing amountof the object is obtained, the process proceeds to Step S203 (Yes inStep S204), and the selected defocusing amount is employed as adefocusing amount to be used in focus control.

On the other hand, when a defocusing amount of the object (for example,the face of a person, or the like) is not obtained, the process proceedsto Step S205 (No in Step S204). It is checked whether or not the imagingapparatus 1000 is in the proximity priority mode. When the imagingapparatus 1000 is in the proximity priority mode, the process proceedsto Step S203 (Yes in Step S205), and the selected defocusing amount isemployed as a defocusing amount to be used in focus control.

When the imaging apparatus 1000 is found not in the proximity prioritymode in Step S205, the process proceeds to Step S406 (No in Step S405),and it is determined whether or not the subject is a moving object.Determining whether or not the subject is a moving object can beperformed using a moving object detection technique of the related art.When the subject is a moving object, the process proceeds to Step S203(Yes in Step S206), and the selected defocusing amount is employed as adefocusing amount to be used in focus control.

On the other hand, when the subject is not a moving object, the processproceeds to Step S207 (No in Step S206). Next, it is checked whether ornot a count value is equal to or greater than a third threshold value inStep S207. When the count value is equal to or greater than the thirdthreshold value, the process proceeds to Step S203 (Yes in Step S207),and the selected defocusing amount is employed as a defocusing amount tobe used in focus control.

On the other hand, when the count value is not equal to or greater thanthe third threshold value, the process proceeds to Step S208 (No in StepS207), and 1 is added to the count value. Then, in Step S209, theselected defocusing amount is not employed, and as a result, focuscontrol using driving of the focus lens based on the defocusing amountis not performed either.

In the stabilization process, when the answers to the all determinationsfrom Step S201 to Step S206 are No, it is the case in which thedefocusing amount is not in the reference, a defocusing amount is notdetected on the object, the imaging apparatus is not in the proximitypriority mode, and the subject is not a moving object. In this case,focus control is not performed until the count value is equal to orgreater than the third threshold value. Accordingly, a stand-by state inwhich focus control is in a paused state until the count value is equalto or greater than the third threshold value can be realized. Inaddition, since focus control is performed based on a defocusing amountas long as the defocusing amount is in the range, a significant changeof the employed defocusing amount can be prevented. When the count valueis equal to or smaller than the third threshold value, 1 is added to thecount value in Step S208, and when the count value is equal to orgreater than the third threshold value, the selected defocusing amountis employed as a defocusing amount to be used in focus control in StepS203. Thus, the length of the stand-by state can be adjusted accordingto setting of the threshold values.

[1-4. Image-plane Defocusing Amount Decision Process]

Next, the image-plane defocusing amount decision process performed inStep S103 of the defocusing amount selection process will be describedwith reference to the flowchart of FIG. 13. The image-plane defocusingamount decision process is performed by the defocusing amount decisionunit 1073. The image-plane defocusing amount decision process is aprocess of deciding defocusing amounts for each image-plane AF area froma focus detection result of the image-plane AF sensor 1031.

First, in Step S301, a maximum value is substituted for an image-planedefocusing amount. Substituting the maximum value for the image-planedefocusing amount corresponds to performing initialization. For example,the image-plane defocusing amount is assumed to be defined as data with16-bit codes. In this case, the range in which the image-planedefocusing amount can be obtained is “−32768 to +32767.” Since“image-plane defocusing amount=maximum value” corresponds toinitialization, the maximum value “+32767” is substituted for theamount. The image-plane defocusing amount substituted with the maximumvalue is called an image-plane defocusing amount for comparison becausethe amount is compared when the sizes of image-plane defocusing amountsobtained for each image-plane AF area are determined.

Next, in Step S202, 1 is added to a variable i for counting the numberof image-plane AF areas (i=i+1). This variable i is a value from 1 tothe maximum number of image-plane AF areas. Thus, when there are 100image-plane AF areas, for example, the image-plane AF areas are numberedfrom 1 to 100, and the variable has a value from 1 to 100. Accordingly,the image-plane defocusing amount decision process is performed on allof the image-plane AF areas by looping the processes of the followingStep S303 to Step S306.

Next, in Step S303, in an image-plane AF area corresponding to thevariable to be processed, it is checked whether or not a luminance valueis equal to or greater than a predetermined value, and thereby it isdetermined whether or not the area has low contrast. When the area isdetermined not to have low contrast, the process proceeds to Step S304(No in Step S303).

Next, in Step S304, the absolute value of an image-plane defocusingamount for comparison is compared to the absolute value of theimage-plane defocusing amount in the image-plane AF area correspondingto the variable i. As a result of the comparison, when the absolutevalue of the image-plane defocusing amount in the i^(th) image-plane AFarea is greater than the absolute value of the image-plane defocusingamount for comparison, the process proceeds to Step S305 (Yes in StepS304). Then, in Step S305, it is set that “the absolute value of theimage-plane defocusing amount for comparison=the absolute value” of theimage-plane defocusing amount, and the defocusing amount of the i^(th)image-plane AF area is decided.

On the other hand, in Step S304, when the absolute value of theimage-plane defocusing amount in the i^(th) image-plane AF area issmaller than the absolute value of the image-plane defocusing amount forcomparison, the process proceeds to Step S306 (No in Step S304) withoutperforming the process of Step S305. In addition, even when the area isdetermined to have low contrast in Step S303, the process proceeds toStep S306 (Yes in Step S303) without performing the process of StepS305. In this case, since the process of Step S305 is not performed, theimage-plane defocusing amount is not decided.

Next, in Step S306, it is determined whether or not the variable ireaches the number of image-plane AF areas. When the variable i does notreach the number of image-plane AF areas, the process proceeds to StepS302 (No in Step S306). Then, the processes from Step S302 to Step S306are repeated until the variable i reaches the number of image-plane AFareas. Accordingly, the processes from Step S302 to Step S306 areperformed on all of the image-plane AF areas.

When the variable i reaches the number of image-plane AF areas, theprocess proceeds to Step S307 (Yes in Step S306). Then, in Step S307, apreviously-decided image-plane defocusing amount determination processis performed.

Herein, the previously-decided image-plane defocusing amountdetermination process will be described with reference to the flowchartof FIG. 14. When approximate defocusing amounts are obtained from aplurality of separate image-plane AF areas, for example, there isconcern that a focus position changes much, and focus is not on a mainsubject. Thus, the previously-decided image-plane defocusing amountdetermination process is a process for preventing a fine change in focusby continuously deciding the image-plane defocusing amounts previouslydecided as image-plane defocusing amounts when image-plane defocusingamounts for each image-plane AF area decided in the previous process areequal to or smaller than a predetermined amount.

First, in Step S401, it is determined whether or not the previouslydecided image-plane defocusing amounts are equal to or smaller than afourth threshold value that is a predetermined threshold value. When theimage-plane defocusing amounts are equal to or smaller than the fourththreshold value, the process proceeds to Step S402 (Yes in Step S401).Then, in Step S402, the previously decided image-plane defocusingamounts are decided as image-plane defocusing amounts again.

On the other hand, in Step S401, when the image-plane defocusing amountsare determined to be equal to or greater than the fourth thresholdvalue, the process proceeds to Step S403 (No in Step S401). Then, inStep S403, defocusing amounts of peripheral image-plane AF areas of theimage-plane AF area for which the previously decided image-planedefocusing amount is obtained are computed.

The peripheral areas are, for example, 8 image-plane AF areas in theperiphery of the image-plane AF areas for which the previously decideddefocusing amounts are computed, four areas in the upper, lower, right,and left sides thereof, or the like.

Next, in Step S404, it is checked whether or not defocusing amounts havebeen computed for all image-plane AF areas in the periphery of theimage-plane AF areas. Regarding the image-plane AF areas in theperiphery, the processes of Step S403 and Step S404 are repeated untilimage-plane defocusing amounts of all of the peripheral image-plane AFareas are computed (No in Step S404).

Then, after the computation of the defocusing amounts is performed forall of the peripheral areas, the process proceeds to Step S405 (Yes inStep S404). Next, in Step S405, it is determined whether a minimum valueof the defocusing amounts of all of the peripheral areas is within thefourth threshold value, and when the value is determined to be withinthe fourth threshold value, the process proceeds to Step S406 (Yes inStep S305).

Then, in Step S406, the minimum value of the defocusing amounts of allof the peripheral areas is decided to be an image-plane defocusingamount. When the previously decided defocusing amounts of theimage-plane AF areas are equal to or greater than the threshold value,the defocusing amount of a peripheral image-plane AF area correspondingto the movement destination of the subject when the subject moves to theperiphery of the areas is employed as an image-plane defocusing amount.

When the minimum value of the defocusing amounts of all of theperipheral areas is determined to be more than the fourth thresholdvalue in Step S405, the image-plane defocusing amount decided in theprocess of the flowchart of FIG. 13 is decided as an image-planedefocusing amount rather than the previously employed image-planedefocusing amount (No in Step S405).

As described above, either of the defocusing amount obtained by thededicated AF sensor 1020 or the defocusing amount obtained by theimage-plane AF sensor 1031 is selected to be used in focus control.Accordingly, autofocus in a wide range by the image-plane AF sensor 1031can be compatible with autofocus with high accuracy by the image-planeAF sensor 1031.

[1-5. Image-Plane Defocusing Amount Correction Process]

Next, a process of increasing accuracy of an image-plane defocusingamount by correcting the image-plane defocusing amount when a subjectleaves all of the dedicated AF areas and is positioned on theimage-plane AF areas as shown in FIG. 7D will be described. FIGS. 15 and16 are flowcharts showing a flow of an image-plane focusing correctionprocess. The image-plane focusing amount correction process is forcorrecting an image-plane defocusing amount based on the differencebetween a defocusing amount obtained by the dedicated AF sensor 1020 anda defocusing amount obtained by the image-plane AF sensor 1031. Theimage-plane focusing amount correction process is performed by thedefocusing amount correction unit 1074.

First, in Step S501, the dedicated AF sensor 1020 and the image-plane AFsensor 1031 respectively perform focus detection. Next, in Step S502, itis determined whether or not focus is on a subject (main subject)targeted by a user among subjects (whether or not a subject to be tracedis decided). When focus is not on the main subject, the process proceedsto Step S503 (Yes in Step S502).

Next, in Step S503, it is checked whether or not the focus detection bythe dedicated AF sensor 1020 has been performed. When the focusdetection by the dedicated AF sensor 1020 has been performed, theprocess proceeds to Step S504, AF control is performed based on thedefocusing amount obtained from the focus detection by the dedicated AFsensor 1020. As long as the focus detection by the dedicated AF sensor1020 is performed, AF control is performed in Step S504 based on thedefocusing amount obtained by the dedicated AF sensor 1020. It should benoted that the AF control in Step S504 corresponds to the AF controlprocess in Step S3 of the flowchart of FIG. 10.

On the other hand, when the focus detection by the dedicated AF sensor1020 has not been performed in Step S503, the process proceeds to StepS505 (No in Step S503). Then, in Step S505, a process for an AFout-of-control time is performed. When AF control is not availablewithout performing the focus detection by the dedicated AF sensor 1020,for example, the imaging apparatus 1000 is in a photographingunavailable state with a nullified release button. Such nullification ofthe release button may be cancelled when, for example, focus detectionis then performed by the dedicated AF sensor 1020.

Description will return to Step S502. When focus is determined to be onthe subject targeted by the user among subjects in Step S502, theprocess proceeds to Step S506 (Yes in Step S502). Next, in Step S503, itis checked whether or not focus detection has been performed by thededicated AF sensor 1020 or the image-plane AF sensor 1031. When thefocus detection is performed by neither the dedicated AF sensor 1020 northe image-plane AF sensor 1031, the process proceeds to Step S505, andthe process for AF out-of-control time is performed (No in Step S506).The process for AF out-of-control time is, for example, nullification ofthe release button as described above. This is because photographing isdifficult to perform when neither the dedicated AF sensor 1020 nor theimage-plane AF sensor 1031 is available to perform focus detection.Nullification of the release button may be cancelled when, for example,focus detection is performed by the dedicated AF sensor 1020 thereafter.

On the other hand, when the focus detection is determined to beperformed by the dedicated AF sensor 1020 or the image-plane AF sensor1031 in Step S506, the process proceeds to Step S507 (Yes in Step S506).Next, in Step S507, it is determined whether or not the main subject isfocused and traced. The determination is possible in such a way that itis checked whether or not there is an area having a focus deviationamount equal to or smaller than a predetermined value, and whether ornot there is an AF area in which focus is substantially on the mainsubject of a previous AF operation among a plurality of AF areas.

When the main subject is not focused or traced, the process proceeds toStep S503 (No in Step S507). Then, if focus detection by the dedicatedAF sensor 1020 is possible in Step S503, AF control is performed basedon a defocusing amount detected by the dedicated AF sensor 1020 in StepS504. In addition, if focus detection by the dedicated AF sensor 1020 isunavailable in Step S503, the process for AF out-of-control time isperformed in Step S505.

When the main subject is confirmed as being traced in Step S507, theprocess proceeds to Step S508 (Yes in Step S507). Next, in Step S508, itis checked whether or not the area in which the main subject is detectedas being traced is a dedicated AF area. When the main subject isdetected in a dedicated AF area, the display unit displays areas of thededicated AF sensor 1020 and the image-plane AF sensor 1031 in StepS509.

In the display of the area in Step S509, for example, crossesoverlapping with the subject among crosses indicating the image-plane AFareas may be indicated by thick lines as shown in FIG. 7D. Thereby, theuser can easily recognize a current subject and areas in which thesubject is detected. In addition, the areas may be displayed by coloringthe crosses overlapping with the subject instead of, or in addition to,the display of the thick lines.

Next, in Step S510, the difference between a defocusing amount in thededicated AF area overlapping with the subject and a defocusing amountin the image-plane AF area is computed, and stored in a storage unit, acache memory, or the like of the imaging apparatus 1000.

As a method for computing the difference, for example, there is a methodfor obtaining the difference of respective defocusing amounts detectedin an overlapping with dedicated AF area and image-plane AF area. Inaddition, the difference may be obtained by associating a defocusingamount of one dedicated AF area and the average of defocusing amounts ofa plurality of image-plane AF areas in the periphery of the dedicated AFarea. Furthermore, the difference of defocusing amounts is also affectedby an aberration property of the photographing lens 1011, and thus when,for example, a subject is positioned apart from substantially the centerof a frame, an offset amount may be added to the difference, consideringan aberration amount of the photographing lens 1011.

As will be described in detail, the difference is used to correct focusadjustment when the main subject leaves all of the dedicated AF areasand is positioned only in the image-plane AF areas.

Next, in Step S504, AF control is performed based on the defocusingamount of the dedicated AF sensor 1020. This is because AF control isbetter performed using the defocusing amount of the dedicated AF sensor1020 when the main subject overlaps with the dedicated AF area since thededicated AF sensor 1020 shows higher AF accuracy than the image-planeAF sensor 1031. Then, the process returns to Step S501.

Description will return to Step S508. When the area in which the subjectis detected as being traced is determined not to be a dedicated AF areain Step S508, the process proceeds to Step S511 (No in Step S508).

The area in which the main subject is being traced is not a dedicated AFarea when the main subject is detected in the image-plane AF areas onlyby the image-plane AF sensor 1031. Thus, next in Step S511, theimage-plane AF area in which the main subject is detected is specified.As a method for specification, for example, an area for which adefocusing amount equal to or smaller than a predetermined value isdetected is specified from a plurality of image-plane AF areas near adedicated AF area in which a main subject has been detected, and asubject detected in the specified area is assumed to be the same subjectas the main subject.

Next, in Step S512, the plurality of image-plane AF areas considered tooverlap with the main subject are grouped, and a predetermined dataprocess such as an averaging process of defocusing amounts detected inthe image-plane AF areas is performed so that tracing of AF is smoothlyperformed.

Next, in Step S513, it is determined whether or not the plurality ofgrouped image-plane AF areas are near the position of the main subjectin the previous process. This is a process for continuing tracing onlywhen the plurality of grouped image-plane AF areas are near the area inwhich the subject is detected in the previous focus detection so thatfocus is not on a subject other than the main subject when the subjectis in the area. Here, being near means, for example, a state in whichareas are neighboring.

When the plurality of grouped image-plane AF areas are near the positionof the main subject in the previous process, the process proceeds toStep S505 (No in Step S513). Then, in Step S505, the process for AFout-of-control time is performed. The process for AF out-of-control timeis the same as described above.

On the other hand, when the plurality of grouped image-plane AF areasare near the position of the main subject in the previous process, theprocess proceeds to Step S514 (Yes in Step S513). Then, in Step S514,using the difference of the defocusing amounts computed and stored inStep S510, the defocusing amount detected by the image-plane AF sensor1031 is corrected.

In general, accuracy of focus detection by the image-plane AF sensor islower than that by the dedicated AF sensor in many cases. Thus, in AFareas of the dedicated AF areas and the image-plane AF areas overlappingwith each other in a state in which the dedicated AF sensor 1020 canperform focus detection, the difference of two focus detection resultsis computed. Then, when a subject overlaps with only image-plane AFareas, focus detection by the image-plane AF sensor 1031 is correctedusing the difference. Accordingly, the sole image-plane AF sensor 1031can perform focus detection with accuracy of the same degree as thededicated AF sensor 1020.

Next, in Step S515, areas traced by the image-plane AF sensor 1031 aredisplayed. In the display of the areas in Step S515, for example,crosses and a frame overlapping with the subject among crossesindicating the image-plane AF sensor 1031 and frames indicating thededicated AF areas may be indicated by thick lines as shown in FIG. 7C.Accordingly, the user can easily recognize areas in which the subject iscurrently detected. In addition, the areas may be displayed by coloringthe crosses and the frame overlapping with the subject instead of, or inaddition to, the display of the thick lines.

Then, in Step S516, AF control is performed based on the correcteddefocusing amount of the image-plane AF sensor 1031. The AF controlcorresponds to the AF control process in Step S3 of the flowchart ofFIG. 10.

As described above, in the image-plane defocusing amount correctionprocess, when both of the dedicated AF sensor 1020 and the image-planeAF sensor 1031 can perform focus detection, the difference between adefocusing amount of the dedicated AF sensor 1020 and a defocusingamount of the image-plane AF sensor 1031 is constantly computed. Then,when a subject leaves all dedicated AF areas and only the image-plane AFsensor 1031 can perform focus detection, the defocusing amount of theimage-plane AF sensor 1031 is corrected using the computed difference.Accordingly, accuracy of focus detection by the image-plane AF sensor1031 can improve, and autofocus with high accuracy and a wide range ofAF areas can be compatible.

<2. Second Embodiment>

[2-1. Configuration of Imaging Apparatus]

Next, a second embodiment of the present technology will be described.

FIG. 17 is a block diagram illustrating another configuration of theimaging apparatus 1000 according to the second embodiment. The imagingapparatus 1000 in the second embodiment has a subject detection unit1076.

The subject detection unit 1076 detects a subject from an image ofsupplied image data. As a subject, for example, there is the face of aperson, or the like. In the second embodiment, a subject is a person,and a case in which the face of the person is detected will beexemplified. However, a target to be detected by the subject detectionunit 1076 does not have to be the face of a person, and animals,buildings, and the like are possible as long as they are detectableobjects.

As a detection method, template matching based on the shape of a face,template matching based on luminance distribution of a face, a methodbased on feature amounts of skin or the face of a person included in animage, and the like can be used. In addition, the methods can becombined in order to increase accuracy in face detection. It should benoted that, since the constituent elements other than the subjectdetection unit 1076 are the same as those of the first embodiment,description thereof will not be repeated.

[2-2. Overview of Process]

Next, a process performed in the second embodiment will be described.First, an overview of a focusing process performed in the presentembodiment will be described with reference to FIGS. 18 to 19. FIG. 18shows a first example of the second embodiment, and FIG. 19 shows asecond example of the second embodiment. FIGS. 18 to 19 show dedicatedAF areas in a photographed screen, image-plane AF areas in thephotographed screen, and subjects traced using autofocus. In FIGS. 18and 19, dashed-lined squares indicate AF areas of the dedicated AFsensor 1020, and dashed-lined crosses indicate AF areas of theimage-plane AF sensor 1031.

In the first example of FIG. 18, the face of a subject to bephotographed is first detected in the photographed screen as shown inFIG. 18A. The face of the subject is positioned on a dedicated AF areaand image-plane AF areas. In this case, focus control is performed usingdefocusing amounts in the areas overlapping with the subject as shown inFIG. 18B. It should be noted that, when the face of the subject overlapswith both dedicated AF areas and image-plane AF areas, focus control maybe performed based on a defocusing amount detected by the dedicated AFsensor 1020. This is because the dedicated AF sensor 1020 exhibitshigher accuracy in focus detection than the image-plane AF sensor 1031.

Then, when focus is on the subject, and then the subject moves as shownin FIG. 18C, focus control is performed based on the defocusing amountof the AF areas in which the subject that has moved is positioned. Inaddition, when the position of the face of the subject leaves all of theAF areas as shown in FIG. 18D, the imaging apparatus 1000 stands byholding the process in a standby state for a predetermined period oftime. In addition, when the subject enters the AF areas again within apredetermined period of time, focus control is performed based on thedefocusing amount of the AF areas in which the face of the subject ispositioned. On the other hand, when the subject does not enter the AFareas within the predetermined period of time, another subjectpositioned in the AF areas is focused on as shown in FIG. 18D.

In the second example of FIG. 19, the face of a subject to bephotographed in the photographed screen is first detected as shown inFIG. 19A. The face of the subject is positioned in image-plane AF areas.In this case, focus control is performed using a defocusing amount ofthe image-plane AF areas overlapping with the face as shown in FIG. 19B.

In addition, when focus is on the subject, and then the subject moves asshown in FIG. 19C, focus control is performed based on the defocusingamount of the AF areas in which the subject that has moved ispositioned. In addition, when the position of the face of the subjectleaves all of the AF areas as shown in FIG. 19D, the imaging apparatus1000 stands by holding the process in a standby state for apredetermined period of time. In addition, when the subject enters theAF areas again within a predetermined period of time, focus control isperformed based on the defocusing amount of the AF areas in which theface of the subject is positioned. On the other hand, when the subjectdoes not enter the AF areas within the predetermined period of time,another subject positioned in the AF areas is focused on as shown inFIG. 19D. It should be noted that the flowchart of the entire process isthe same as that of the first embodiment shown in FIG. 10.

[2-3. Defocusing Amount Selection Process]

Next, the defocusing amount selection process included in the overallflowchart described above will be described with reference to theflowcharts of FIGS. 20 and 21. Since the processes other than those inSteps S1001 to S1006 in the flowcharts of FIGS. 20 and 21 are the sameas those in the first embodiment, description thereof will not berepeated.

After an image-plane defocusing amount decision process is performed inStep S1001, the process proceeds to Step S1002. It should be noted thatthe image-plane defocusing amount decision process of the secondembodiment will be described later in detail. However, the image-planedefocusing amount decision process of the second embodiment is also aprocess in which defocusing amounts are computed for each of a pluralityof image-plane AF areas and an image-plane defocusing amount is decidedin the same manner as in the first embodiment.

Next, in Step S1002, it is determined whether or not the face of asubject has been detected in a photographed screen. When the face hasnot been detected, the process proceeds to Step S104 (No in Step S1002).

On the other hand, when the face has been detected, the process proceedsto Step S1003 (Yes in Step S1002). Next, in Step S1003, it is determinedwhether or not the detected face overlaps with dedicated AF areas. Whenthe face overlaps with the dedicated AF areas, a minimum defocusingamount among the defocusing amounts of the dedicated AF areas located inthe region detected as the face is set to be a selected defocusingamount in Step S1004 (Yes in Step S1003).

When the detected face does not overlap with the dedicated AF areas inStep S1003, the process proceeds to Step S1005 (No in Step S1004). Next,in Step S1005, it is determined whether or not the detected faceoverlaps with image-plane AF areas. When the face overlaps with theimage-plane AF areas, a minimum defocusing amount among the defocusingamounts of the plurality of image-plane AF areas located in the regiondetected as the face is set to be a selected defocusing amount in StepS1006 (Yes in Step S1005).

Since other processes are the same as those of the first embodiment,description thereof will not be repeated. It should be noted that astabilization process is also the same as that of the first embodiment.

Next, an image-plane defocusing amount decision process in the secondembodiment will be described with reference to the flowchart of FIG. 22.It should be noted that, since processes other than those in Steps S3001to S3004 in the flowchart of FIG. 22 are the same as those in the firstembodiment, description thereof will not be repeated.

First, in Step S3001, a maximum value is substituted for an image-planeface defocusing amount. The image-plane face defocusing amount refers toa defocusing amount of image-plane AF areas overlapping with a regiondetected as the face of a subject in a photographed screen. Substitutingthe maximum value for the image-plane face defocusing amount correspondsto performing initialization. For example, the image-plane facedefocusing amount is assumed to be defined as data with 16-bit codes. Inthis case, the range in which the image-plane face defocusing amount canbe obtained is “−32768 to +32767.” Since “image-plane face defocusingamount=maximum value” corresponds to initialization, the maximum value“+32767” is substituted for the amount. The image-plane face defocusingamount substituted with the maximum value is called an image-plane facedefocusing amount for comparison because the amount is compared when thesizes of image-plane defocusing amounts obtained for each image-plane AFarea overlapping with a face region are determined.

In addition, in Step S3001, the maximum value is substituted for animage-plane defocusing amount for comparison in the same manner as inthe first embodiment. In Step S302, substituting 1 for a variable i isalso the same as in the first embodiment.

In Step S303, when the area is determined not to have low contrast, theprocess proceeds to Step S3001 (No in Step S303). Next, in Step S3002,it is checked whether or not an image-plane AF area among the pluralityof image-plane AF areas corresponding to the variable i overlaps withthe region detected as the face.

When the image-plane AF area corresponding to the variable i overlapswith the face region, the process proceeds to Step S3003 (Yes in StepS3002). Next, in Step S3003, the absolute value of the image-plane facedefocusing amount for comparison is compared to the absolute value ofthe image-plane defocusing amount in an i^(th) image-plane AF area. As aresult of the comparison, when the absolute value of the image-planedefocusing amount in the i^(th) image-plane AF area is smaller than theabsolute value of the image-plane face defocusing amount for comparison,the process proceeds to Step S3004 (No in Step S3003). Then, in StepS3004, the defocusing amount of the i^(th) image-plane AF areaoverlapping with the face region is decided.

On the other hand, when the absolute value of the image-plane defocusingamount in the i^(th) image-plane AF area is greater than the absolutevalue of the image-plane face defocusing amount for comparison in StepS3003, the process proceeds to Step S304 (Yes in Step S3003) withoutperforming the process of Step S3004. In addition, when the image-planeAF area corresponding to the variable i overlaps with the face region inStep S3002, the process also proceeds to Step S304 (Yes in Step S3002)without performing the process of Step S3004. Since the process of StepS3004 is not performed in this case, the image-plane defocusing amountof the i^(th) image-plane AF area overlapping with the face regionremains undecided. As described above, in the second embodiment, thedefocusing amount of the image-plane AF area overlapping with the regiondetected as the face is decided.

The processes in the second embodiment are performed as described above.In the second embodiment, since focus control is performed based on thedefocusing amount of the AF area overlapping with the region detected asthe face of the subject, focus control is possible based on the facepositions as shown in FIGS. 18 to 19.

The processes in the present technology are performed as describedabove. In general, when a subject leaves all AF areas of the dedicatedAF sensor 1020 in a state in which the subject has been focused andtraced, there are cases in which another subject present in thebackground of the subject targeted by a user is focused on. However,according to the present technology, since a subject can be detected bythe image-plane AF sensor 1031 in a wide range, focus can be kept on thesubject once the subject is focused even when the subject leaves all AFareas of the image-plane AF sensor 1031, and erroneous focusing onanother subject can be prevented.

In addition, when a tracing operation is performed with the focus on asubject who a user desires and another subject approaches and enters theframe, there are cases in which the latter subject is focused on.However, according to the present technology, once focus is on asubject, the focus is not shifted to another subject even when thesubject approaches, and the focus can be continuously on the subject whothe user desires.

In addition, since the image-plane AF sensor 1031 having a wide focusrange is used in addition to the dedicated AF sensor 1020, even when aposition of a subject is significantly changed, the subject can bereliably detected and traced. Furthermore, when the face or the like ofa subject is detected, and the face or the like overlaps withimage-plane AF areas, focus control is performed using image-planedefocusing amounts thereof, and thus a subject can be traced in a moreextensive range than before.

<3. Modified Example>

Hereinabove, although the embodiments of the present technology havebeen described in detail, the present technology is not limited to theembodiments described above, and can be variously modified based on thetechnical gist thereof.

Additionally, the present technology may also be configured as below.

(1)

An imaging apparatus including:

a first focus detection unit that has a plurality of first focusdetection areas in a photographed screen, and detects a first defocusingamount in the first focus detection areas;

a second focus detection unit that has a plurality of second focusdetection areas in a photographed screen, and detects a seconddefocusing amount in the second focus detection areas;

a defocusing amount selection unit that selects which of the firstdefocusing amount detected by the first focus detection unit and thesecond defocusing amount detected by the second focus detection unit isused; and

a focus control unit that performs focus control by moving a focus lenson the basis of the defocusing amount selected by the defocusing amountselection unit.

(2)

The imaging apparatus according to (1),

wherein, when a subject overlaps with the first focus detection areasand the second focus detection areas, the defocusing amount selectionunit selects the first defocusing amount.

(3)

The imaging apparatus according to (1) or (2),

wherein, when the imaging apparatus is in a proximity priority mode, thedefocusing amount selection unit selects the first defocusing amount.

(4)

The imaging apparatus according to any one of (1) to (3), furtherincluding:

a defocusing amount decision unit that decides the second defocusingamount corresponding to each of the plurality of second focus detectionareas.

(5)

The imaging apparatus according to (4),

wherein, when the second focus detection unit detects the seconddefocusing amount, the defocusing amount decision unit compares thesecond defocusing amount that has been previously decided with athreshold value, and when the second defocusing amount that has beenpreviously decided is smaller than or equal to the threshold value, thedefocusing amount decision unit decides the second defocusing amountthat has been previously decided as a second defocusing amount.

(6)

The imaging apparatus according to any one of (1) to (5),

wherein, when the second focus detection unit detects the firstdefocusing amount, the defocusing amount decision unit compares thesecond defocusing amount that has been previously decided with athreshold value, and when the second defocusing amount that has beenpreviously decided is greater than or equal to the threshold value, thedefocusing amount decision unit decides, as the second defocusingamount, a smallest value in defocusing amount in a peripheral area ofthe second focus detection areas corresponding to the detected seconddefocusing amount.

(7)

The imaging apparatus according to any one of (1) to (6), furtherincluding:

a defocusing amount correction unit that corrects the second defocusingamount detected by the second focus detection unit.

(8)

The imaging apparatus according to any one of (1) to (7),

wherein, when the subject overlaps with the first focus detection areasand the second focus detection areas, the defocusing amount correctionunit computes a difference between the first defocusing amount and thesecond defocusing amount, and thereafter, when the subject overlaps withonly the second focus detection areas, the defocusing amount correctionunit uses the difference to correct the second defocusing amount.

(9)

The imaging apparatus according to any one of (1) to (8), furtherincluding:

a subject detection unit that detects a subject from a photographedimage,

wherein, when the first focus areas overlap with a region detected bythe subject detection unit as a subject, the defocusing amount selectionunit selects the first defocusing amount.

(10)

The imaging apparatus according to any one of (1) to (9),

wherein, when not the first focus areas but the second focus areasoverlap with a region detected by the subject detection unit as asubject, the defocusing amount selection unit selects the seconddefocusing amount.

(11)

The imaging apparatus according to any one of (1) to (10),

wherein the first focus detection unit is a dedicated phase differencefocus detecting module.

(12)

The imaging apparatus according to any one of (1) to (11),

wherein the second focus detection unit is a phase difference focusdetecting element provided in an image sensor.

(13)

The imaging apparatus according to any one of (1) to (12),

wherein positions of the second focus detection areas are unevenlydisposed in the photographed screen in a manner that the first focusdetection areas are associated therewith.

(14)

The imaging apparatus according to any one of (1) to (13),

wherein, when the first focus detection unit fails in detecting thefirst defocusing amount and the second focus detection unit fails indetecting the second defocusing amount, the imaging apparatus nullifiesa photographing operation.

(15)

A focus control method including:

selecting which of a first defocusing amount and a second defocusingamount is used, the first defocusing amount being detected by a firstfocus detection unit that has a plurality of first focus detection areasin a photographed screen, the second defocusing amount being detected bya second focus detection unit that has a plurality of second focusdetection areas in a photographed screen; and

performing focus control by moving a focus lens on the basis of theselected defocusing amount.

REFERENCE SIGNS LIST

-   1000 imaging apparatus-   1020 dedicated AF sensor-   1031 image-plane AF sensor-   1072 defocusing amount selection unit-   1073 defocusing amount decision unit-   1074 defocusing amount correction unit-   1075 focus control unit-   1076 subject detection unit

The invention claimed is:
 1. An imaging apparatus, comprising: a firstfocus detection sensor that has a plurality of first focus detectionareas in a photographed screen, and configured to detect a firstdefocusing amount in the plurality of first focus detection areas; asecond focus detection sensor that has a plurality of second focusdetection areas in the photographed screen, and configured to detect asecond defocusing amount in the plurality of second focus detectionareas; and one or more circuits configured to: set a second defocusingamount that has been previously decided as the second defocusing amountbased on a comparison of the previously decided second defocusing amountwith a threshold value; select which of the first defocusing amount orthe second defocusing amount is used; and control focus by movement of afocus lens based on the selected defocusing amount.
 2. The imagingapparatus according to claim 1, wherein, when a subject overlaps withthe plurality of first focus detection areas and the plurality of secondfocus detection areas, the one or more circuits are further configuredto select the first defocusing amount.
 3. The imaging apparatusaccording to claim 1, wherein, when the imaging apparatus is in aproximity priority mode, the one or more circuits are further configuredto select the first defocusing amount.
 4. The imaging apparatusaccording to claim 1, wherein one or more circuits are furtherconfigured to decide the second defocusing amount that corresponds toeach of the plurality of second focus detection areas.
 5. The imagingapparatus according to claim 1, wherein, when the second focus detectionsensor detects the second defocusing amount, the one or more circuitsare further configured to compare the previously decided seconddefocusing amount with the threshold value, and when the previouslydecided second defocusing amount is smaller than or equal to thethreshold value, the one or more circuits are further configured to setthe previously decided second defocusing amount as the second defocusingamount.
 6. The imaging apparatus according to claim 1, wherein, when thesecond focus detection sensor detects the second defocusing amount, theone or more circuits are further configured to compare the previouslydecided second defocusing amount with the threshold value, and when thepreviously decided second defocusing amount is greater than or equal tothe threshold value, the one or more circuits are further configured toset, as the second defocusing amount, a smallest value in defocusingamount in a peripheral area of the plurality of second focus detectionareas that corresponds to the detected second defocusing amount.
 7. Theimaging apparatus according to claim 1, wherein the one or more circuitsare further configured to: correct the detected second defocusingamount.
 8. The imaging apparatus according to claim 7, wherein, when asubject overlaps with the plurality of first focus detection areas andthe plurality of second focus detection areas, the one or more circuitsare further configured to compute a difference between the firstdefocusing amount and the second defocusing amount, and when the subjectoverlaps with the plurality of second focus detection areas, the one ormore circuits are further configured to use the difference to correctthe second defocusing amount.
 9. The imaging apparatus according toclaim 1, wherein the one or more circuits are further configured to: asubject from a photographed image; and when the plurality of first focusdetection areas overlap with a region detected as the subject, selectthe first defocusing amount.
 10. The imaging apparatus according toclaim 9, wherein, when the plurality of second focus detection areasoverlap with the region detected as the subject, the one or morecircuits are further configured to select the second defocusing amount.11. The imaging apparatus according to claim 1, wherein the first focusdetection sensor is a dedicated phase difference focus detecting module.12. The imaging apparatus according to claim 1, wherein the second focusdetection sensor is a phase difference focus detecting element providedin an image sensor.
 13. The imaging apparatus according to claim 1,wherein positions of the plurality of second focus detection areas areunevenly disposed in the photographed screen in a manner that theplurality of first focus detection areas are associated therewith. 14.The imaging apparatus according to claim 1, wherein, when the firstfocus detection sensor fails in detection of the first defocusing amountand the second focus detection sensor fails in detection of the seconddefocusing amount, the imaging apparatus is configured to nullify aphotographing operation.
 15. A focus control method, comprising:selecting which of a first defocusing amount and a second defocusingamount is used, wherein the first defocusing amount is detected by afirst focus detection sensor that has a plurality of first focusdetection areas in a photographed screen, and the second defocusingamount is detected by a second focus detection sensor that has aplurality of second focus detection areas in the photographed screen;wherein a previously set second defocusing amount is decided as thesecond defocusing amount based on a comparison of the previously decidedsecond defocusing amount with a threshold value; and controlling focusby movement of a focus lens based on the selected defocusing amount. 16.An imaging apparatus, comprising: a first focus detection sensor thathas a plurality of first focus detection areas in a photographed screen,and configured to detect a first defocusing amount in the plurality offirst focus detection areas; a second focus detection sensor that has aplurality of second focus detection areas in the photographed screen,and configured to detect a second defocusing amount in the plurality ofsecond focus detection areas; and one or more circuits configured to:correct the detected second defocusing amount, wherein when a subjectoverlaps with the plurality of first focus detection areas and theplurality of second focus detection areas, the one or more circuits arefurther configured to compute a difference between the first defocusingamount and the second defocusing amount, and when the subject overlapswith only the plurality of second focus detection areas, the one or morecircuits are further configured to use the difference to correct thesecond defocusing amount; select which one of the first defocusingamount or the second defocusing amount is used; and control focus bymovement of a focus lens based on the selected defocusing amount.